Busbar holders are generally offered today in the form of one-piece plastic castings. This entails the problem that only busbars of one particular size can be associated with one busbar holder, and holders for various sizes of busbar must on the whole be kept on hand. Thus, the available busbar holders of this type necessarily demand a considerable inventory. It is also impossible to assemble various busbars into one holder of this type. Furthermore, the distance between busbars in known busbar holders cannot be varied as desired, and the user is even warned to leave one empty holder between two full ones.